Light source

ABSTRACT

A compact, short arc, high-pressure, xenon-filled light source provides high-intensity radiation with reliability and tolerance of severe environments. Specially shaped thoriated tungsten electrodes are fixed in opposed relation to nickel support blocks welded within a composite, uniform diameter, cylindrical envelope portion formed of a tube of alumina ceramic sealed to nickeliron-cobalt alloy sleeves.

I United States Patent 1151 3,636,395 Banes, Jr. et al. 1 Jan. 18, 1972[54] LIGHT SOURCE 3,136,915 6/1964 Jaatinen ..313 231 [72] Inventors:Nathan M. Banes, Jr.; James H. Bottcher, 3346351 10/1967 Llenhind"man/32 both ofoainesviue Fla. 3,378,713 4/1968 Ludw1g ..313/323,289,027 1111966 Jones ..3l3/231 [73] Assignee: Sperry Rand Corporation3,480,829 11/1969 Van Omum ..315/1 1 1 22 F1 d: F h. 19 1970 l I e ePrimary Examiner-Herman Karl Saalbach [21] App]. No.: 12,655 AssistantExaminer-C. Baraff Anome S. C. Yeaton [52] U.S.Cl..3l3/8,3l3/l08,3l3/ll2,

3131184, 313/217, 313 249 [571 ABSTRACT [51] Int. Cl. ..H0lj6l/98 A compact, short arc, high pressure, xenon-filled light source [58] held ofSearch 13/25 l provides high-intensity radiation with reliability andtolerance 313/221 8 of severe environments. Specially shaped thoriatedtungsten electrodes are fixed in opposed relation to nickel support [56]References cued blocks welded within a composite, uniform diameter,cylindrin- STATES PATENTS cal envelope portion formed of a tube ofalumina ceramic sealed to nickel-iron-cobalt alloy sleeves. 3,054,9219/1962 Lye ..313/32 3,256,383 6/1966 Sasorov ..3 1 3/32 8 Claims, 1Drawing Figure I90 90 18a H0 360 20a) 2/ INVENTORS NATHAN M Ell/V55 JRJAMES H. BOTTCHEI? BY ATTORNEY PATENTEU JAN 1 8 I972 LIGHT SOURCEBACKGROUND OF THE INVENTION 1. Field of the Invention The inventionpertains to high-intensity sources of optical radiation in theultraviolet, visible, or infrared regions and more particularly relatesto such light sources in which electrical power is converted intohigh-intensity light in an electrical current discharge between closelyspaced electrodes within an ionized gas maintained at high pressure.

2. Description of the Prior Art Short arc, high-pressure light sourceshave been available in the past in which an electrical discharge in anionized noble gas is employed as a light source. Light sources of thistype have conventionally been constructed using bulbous quartz envelopesin which electrode structures have been mounted by using expensivecombinations of graded quartz-to-glass and glass-to-metal sealingtechniques. Assembly of the light source requires highly skilled glassworkers to form graded seals reliable enough to withstand the highinternal gas pressure needed for efficient operation of the lightsource, a pressure on the order of 30 atmospheres. Problems withreliability and reproducible performance are often encountered. A highdegree of human craftsmanship is needed to build such light sources, buteven with highly skilled personnel, precise reproducibility is notachieved. Lack of reproducibility is especially observed in relativelyhigh failure rates under severe environmental stress.

SUMMARY OF THE INVENTION The present invention is a compact, short arc,high-pressure, xenon-filled, high-intensity electrical discharge lightsource avoiding the disadvantages of prior art short are light sources.Use of brazed and welded components in the construction of theelectrodes and of the pressure envelope for the light source makes itpossible greatly to increase the internal operating gas pressure,resulting in an increase in efficiency of light generation, better arcstability, and high reproducibility in manufacture. A uniform diametertubular envelope is formed of an alumina ceramic brazed at its ends tonickeliron-cobalt sleeves. The pressure envelope is completed byelectrode-supporting nickel cylinders welded within thenickel-iron'cobalt sleeves and supporting shaped electrodes of thoriatedtungsten. The shaped electrodes are additionally spring supported toafford immunity from the effects of shock or vibration. Theelectrode-supporting nickel cylinders and the enlarged portions of theelectrodes serve to reduce the volume occupied by gas within the lightsource, to protect the seals between the alumina ceramic and thenickel-iron-cobalt sleeves from direct thermal radiation, and also toprovide long heat paths for the protection of the seals and for theimproved regulation of the operating temperature of the conical arcelectrode tips.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described indetail with reference to the sole FIGURE, which is a longitudinalcross-sectional view of the short are light source of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the sole FIGURE, there isillustrated a novel short are, high-pressure, high-intensity lightsource comprising a uniform diameter composite envelope unit 1, an anodeassembly 2, and a cathode assembly 3, sealed together in ordercooperatively to provide a complete high-pressure envelope.

Envelope unit 1 comprises a cylindrical tube of translucent ortransparent alumina ceramic or other suitable material. The material ofcylinder 10 may be any suitable alumina ceramic, including a materialmanufactured by the Coors Porcelain Company comprising a 99.9 percentalumina of polycrystalline structure. Transparent sapphire may be used.

The parallel ends 9 and 9a of cylinder 10 are provided in a conventionalway with a metal surface readily bonded to the alumina by well-knownmeans. The envelope unit 1 is completed by tubular cylinders 11 and 11a,which are respectively sealed at 9 and 9a by brazing with pure silver.The material of metal-to-ceramic seal forming cylinders 11, 11a, may beany of several available nickel-iron-cobalt alloys suitable for thepurpose. As seen in the FIGURE, the inner and outer diameters of thetubular ceramic cylinder 10 and of the tubular nickel-iron-cobalt alloycylinders 11, Ila sealed thereto atjunctions 9 and 9a respectively matcheach other.

The anode assembly 2 and the cathode assembly 3 of the novel lightsource are affixed within the composite envelope unit 1 in substantiallymirror image relation about the plane A-A, which plane is located in thecenter of the arc discharge to be generated within the light source. Forexample, the anode assembly 2 and the cathode assembly 3 are providedwith conically tipped electrode elements 12 and 12a substantiallyequally spaced on either side of the plane A-A.

Referring now to the anode assembly 2, the conically tipped electrodeunit 12 is comprised of a cone 13 supported on a solid cylinder 14 whosediameter is small relative to the inner diameter of the compositeenvelope unit 1 and is also equal to the diameter of the base of conel3. Anode element 12 is composed of a known 2 percent thoriated tungstenmaterial and is centrally attached at the circular flat face 15 of asolid cylinder 16 having almost the same external diameter as theinternal diameter of composite envelope unit 1. Support cylinder 16extends from the face 15 past the junction 9 in envelope unit 1 to face17. From face 17, a smaller cylinder or rod 18 projects axially.

The end 19 of the composite envelope unit 1 is closed by a shapedcylindrical block 20 made of nickel and having two primary functions;one function is to support the rod 18 and thus to support cylinder 16and electrode 12 in fixed relation along the longitudinal axis of thelight source structure. For example, cylinder 18 may be affixed within abore 21 in the face 22 of block 20 by brazing with a conventionalbrazing alloy such as the 92 percent gold, 8 percent palladium alloy.The second significant function performed by cylindrical block 20 is tocomplete the pressure envelope at end 19 of the structure. For thispurpose, a portion of cylindrical block 20 has a diameter substantiallyequal to the inner diameter of nickel-iron-cobalt alloy sleeve 11. Thenickel block 20 is thus readily fastened within alloy sleeve 11 by usingany suitable welding process to form an annular weldment 23 sealing theinterface between block 20 and sleeve 11 at end 19.

Anode assembly 2 is further supported in fixed relation to the compositeenvelope unit 1 by a toroidal spring element 25 located in an annulargroove 26 adjacent surface 15 of surface electrode 16, spring element 25being comprised of a wire coil made of known tungsten-rhenium alloy. Thecoiled spring 25 is coiled within a groove 26 in support 16 to form atoroid. The inner portion of coiled spring 25 contacts the valley ofgroove 26, while the outer portion of spring 25 presses firmly againstthe inner wall 27 of the ceramic sleeve 10. The toroidal spring 25 isdesigned as to stiffness and other properties such as to aid in thesupport of the interior portion of anode assembly 2, and more especiallyto aid in mechanically stabilizing the anode assembly so that theconical electrode 12 may remain in fixed relation to its cooperatingconical electrode 12a under conditions of shock and vibration.

Anode assembly 2 is supplied with an axial nickel rod 30 sealed bybrazing at surface 31 using, for example, a 92 percent gold, 8 percentpalladium brazing alloy, within an axial bore in cylindrical block 20.Rod 30 extends axially beyond the end 19 sufficiently to serve as anelectrical terminal. For example, a nickel anode lead 33 may be fastenedto the surface of rod 30, as by spot welding.

Referring now to the cathode assembly 3 opposite anode assembly 2, theconically tipped electrode unit 12a is composed of a cone 13a supportedon a solid cylinder 14a whose diameter is small relative to the innerdiameter of the composite envelope unit 1 and is also equal to thediameter of the base cone 13a. Cathode element 120 is composed of 2percent thoriated tungsten and is axially or centrally attached at thecircular face 15a of a solid support cylinder 16a having almost the sameexternal diameter as the internal diameter of composite envelope unit 1.Cylinder 16a extends from the face 15a past junction or seal 9a ofenvelope unit 1 to the face 170.

From face 17a, a smaller cylinder 18a projects centrally. The end 19a ofthe composite envelope unit 1 is closed by a shaped cylindrical block20a of nickel and having two primary functions: one function is tosupport rod 18a and thus to support cylinder 16a and electrode 12a infixed relation along the longitudinal axis of the structure. Forexample, cylinder 18a may be affixed within a bore in the face 22a ofblock 20a by brazing with a conventional brazing alloy such as a 92percent gold, 8 percent palladium alloy. The second significant functionperformed by block 20a is to complete the pressure envelope at end 19aof the light source. For this purpose, a portion of the cylindricalblock 20a has a diameter substantially equal to the inner diameter ofnickel-iron-cobalt alloy sleeve 11a. Block 11a is thus readily fastenedwith alloy sleeve 2011 by using any suitable welding process to form anannular weldment 23a sealing the interface between block 20a and sleeve11a at end 19a.

Cathode assembly 3 is further supported in fixed relation to thecomposite envelope unit 1 by a spring element 251: located in an annulargroove 26a adjacent surface 15a of electrode support 16a, spring element25a being comprised. of a wire coil made of a known tungsten-rheniumalloy. As seen by comparing the cross-sectional view of support 16a andspring 25a with the analogous parts of support 16, the coiled spring 25ais coiled within a groove 26:: to form a toroid; the inner portion ofcoiled spring 25a contacts the valley of groove 26a, while the outerportion of spring 25a presses firmly against the inner wall 27 of theceramic sleeve 10. The spring 25a is designed as to stiffness and otherproperties such as to aid in the support of the interior portion ofcathode assembly 3, and more especially further to aid in mechanicallystabilizing the cathode assembly 3 so that the conical electrode 12a mayremain in fixed relation to its counterpart electrode 12 underconditions of shock and vibration.

The shapes and dimensions of the cooperating electrodes 12 and 1211 aredictated by several considerations. The temperature of the tips ofelectrode cones 13, 13a must be as high as possible without melting thethoriated tungsten material of which they are composed. This selectionresults in a relatively higher temperature for the gas plasma in thevolume of the arc and therefore, an increase in light output.Furthermore, it is desirable to step the support cylinder 16 and 16adiameters to a large diameter to protect seals 9, 9a from directradiation, to provide a substantial heat sink path, and also to reducethe total gas volume within the structure. With reduced gas volume, thearc temperature builds up rapidly and the smaller gas volume produces adesirable higher gas pressure. Also, as a consequence of the reducedvolume, convection currents which would otherwise be relatively free tobuild up and to cool the arc plasma are minimized.

The cathode assembly 3 departs from being a mirror image form of anodeassembly 2 in thatcathode assembly 3 provides means for an externalelectrical connection, as does assembly 2, but cathode assembly 3particularly provides means for filling the light source interior withan appropriate noble gas. Such means concerns modifications in thecylindrical block 20a whereby passageways are provided for flow of gasrelative to the interior of the light source.

The clearance space coupled past face 22a of cylindrical block 20a isdually coupled to a radial bore 36, 36a extending diametrically acrossblock 20a. An axial bore 37 extends at least from bore 36, 36a to theexterior of cylindrical block 2011. A portion of axial bore 37 isfurther enlarged to support a copper tube 38 sealed therewithin. Coppertube 38 is brazed to the nickel cylindrical block 20a by thegold-palladium alloy used in other brazed joints of the structure. Whenthe interior of the light source is filled with a suitable gas, the end39 of tube 38 is pinched off in a manner commonly used in the vacuumtube art, thus completing the envelope of the structure. A nickelcathode lead 33a may be conveniently affixed to the surface of tube 38.q

The light source is constructed in a manner affording predictableperformance, good reliability, and tolerance of severe environmentsthrough the use of construction techniques employing simultaneousforming of brazed joints. Parts of the structure involving fabricationof metal-to-ceramic seals 9 and 9a which must be assembled underconditions not compatible with the brazing operations are formedseparately by noncritical processes. Seals 9 and 9a are readily formed,for example, by reliable automatic machines. The units of the structureare designed for final welding at points remote from the metal-toceramicseals 9, 9a. Graded glass or quartz seals are entirely avoided.

For example, the anode parts including the thoriated tungsten electrode12, electrode support 16, and rod 18, the cylindrical end block 20, andthe anode terminal rod 30 are finished and then brazed together to forma composite structure using the aforementioned gold-palladium alloy in afurnace operated for about one-half an hour at substantially l,240 C.The corresponding parts of cathode assembly '3 are similarly madeunitary. The composite envelope unit 1 is formed using established sealfabrication techniques by brazing ends of the nickel-iron-cobaltcylinders 11, lla with pure silver at the ends 9, 9a of ceramic cylinder10 at 960 C. using a conventional procedure.

Now, the respective cathode; and anode assemblies 2 and 3 are slidwithin envelope assembly after springs 25, 2511 are put in place, and ahelium arc weld is made at locations 23 and 23a substantially tocomplete the structure. The helium arc welding method permits rapidoperation with only local heat paths in nickel-ironcobalt tubes 11, 1la. The structure is sub jected to baking for about 2 hours at 400 to500 C. to remove all contaminants within its interior. The consequentmaintenance of the purity of the gas to be put in the lamp interior hasbeen demonstrated to add to the intensity of the light output.

After returning to room temperature, the light source is evacuated andis then coupled via copper tube 38 to a highpressure container of purexenon gas, the container being equipped with a calibrated pressure gage,and the lamp is filled with xenon to a pressure level. of substantially27 atmospheres. Copper tube 38 is then pinched off and the light sourceis ready to be operated. The brazed construction of the light sourcemakes it possible to increase the internal gas pressure from the priorart level of l7 atmospheres, permitting a corresponding increase inoutput light level and better arc stability. The increased cold" gaspressure from the prior 17 atmospheres to substantially 27 atmospherespermits a great increase in the hot" or operating pressure within thelamp, and is largely responsible for the increase of about 15 percent inlight output in the inventive lamp, for example, from the prior art 2.6watts per steradian to 3.0 watts per steradian.

In operation, the arc discharge in the light source may be started inconventional fashion, for example, by the initial application to leads33, 33a of a relatively high-voltage starting pulse on the order of15,000 volts. Once the xenon gas is ionized, the arc discharge isreadily maintained by a much lower voltage of the order of 30 volts, forexample. Other applicable means of starting short arc lamps are known tothe art.

The novel source provides a light output 10 to 20 percent greater thanprior art lamps such as those which, for example, have customarily usedgraded-seal quartz envelopes. Higher light intensities result from theuse of the improved pressure envelope, improved electrode construction,a relatively small volume of gas, and high-temperature bake-outpermitting maximum internal cleanliness and thus also ensuringreproducibility and long life.

In addition to achieving a major performance improvement over previouslight source designs, the invention presents a design much more suitedto mass production, in that many manual steps in manufacture areeliminated. For example, the manufacture of graded seals required in theprior art quartz lamp is avoided and the lamp interior is easily filledwith an accurately known amount of xenon gas, whereas the prior artquartz lamp must be filled by introducing into the cooled lamp aquantity of zenon cooled to liquid form because the quartz envelopecannot be tipped off at high pressure.

The uniform diameter of the light source envelope facilitates packagingin shipment and within equipment in which the light source is employed.Of major significance is the configuration of the nickel cylinders andthe shaped electrodes such that gas volume is reduced, thealumina-to-metal seals are protected by long heat conduction paths andfrom direct thermal radiation, and the temperatures of the electrodecones are appropriately regulated.

While the invention has been described in its preferred embodiment, itis to be understood that the words that have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

We claim:

1. A gas-filled electrical light source comprising:

a substantially uniform diameter tube of ceramic material transparent tolight generated by said light source and having first and second ends,

first and second substantially circular metal tubes respectivelypermanently bonded in hermetically sealed abutting relation to saidceramic tube at said respective first and second ends of said ceramictube,

first and second electrode support means permanently bonded within saidrespective first and second metal tubes at ends thereof remote from saidfirst and second ends of said ceramic tube for completing an envelopeadapted to contain gas under pressure,

first and second electrode means fixedly supported within said gasenvelope by said respective electrode support means and mutually alignedin cooperative light-generating relation for radiation of light througha central portion of said ceramic tube,

said electrode support means having circumferential grooves adjacentsaid electrodes, and

spring means mounted within said grooves contacting said ceramic tubefor resiliently supporting said electrodes within said ceramic tube.

2. Apparatus as described in claim I wherein:

said first and second electrode support means each comprise at, leastfirst and second successive collinear portions of respective small andlarge diameters for regulation of heat flow along said electrode supportmeans from said electrode means, and

said first and second electrode means are supported directly from saidrespective large diameter portions.

3. Apparatus as described in claim 2 wherein:

said electrode means are substantially smaller in diameter than saidlarge diameter portions of said electrode support means.

4. Apparatus as described in claim 3 wherein said portions of largerdiameter of said electrode support means and said electrode means are soconstructed and arranged within said gas envelope that said permanentlysealed first and second ends of said ceramic tube are shielded fromdirect radiation of light generated by said electrode means.

5. Apparatus as described in claim 3 wherein each said electrode meansis provided with a conical end comprising thoriated tungsten.

6. Apparatus as described in claim 5 wherein:

said gas envelope contains a noble gas, and

said electrode support means and said electrode means occugy a majorityportion of the interior of said electrical lrg source, a mrnonty portionof said rntenor being occupied by said noble gas for providing highoperating gas pressure.

7. Apparatus as described in claim 5 wherein:

said ceramic material is comprised of polycrystalline alumina, and

said metal tubes are comprised of an iron-nickel-cobalt alloy adapted topermanent hermetic scaling to polycrystalline alumina.

8. Apparatus as described in claim 7 wherein:

said electrode support means are comprised of nickel, and

said spring means are comprised of a tungsten-rhenium alloy.

2. Apparatus as described in claim 1 wherein: said first and secondelectrode support means each comprise at least first and secondsuccessive collinear portions of respective small and large diametersfor regulation of heat flow along said electrode support means from saidelectrode means, and said first and second electrode means are supporteddirectly from said respective large diameter portions.
 3. Apparatus asdescribed in claim 2 wherein: said electrode means are substantiallysmaller in diameter than said large diameter portions of said electrodesupport means.
 4. Apparatus as described in claim 3 wherein saidportions of larger diameter of said electrode support means and saidelectrode means are so constructed and arranged within said gas envelopethat said permanently sealed first and second ends of said ceramic tubeare shielded from direct radiation of light generated by said electrodemeans.
 5. Apparatus as described in claim 3 wherein each said electrodemeans is provided with a conical end comprising thoriated tungsten. 6.Apparatus as described in claim 5 wherein: said gas envelope contains anoble gas, and said electrode support means and said electrode meansoccupy a majority portion of the interior of said electrical lightsource, a minority portion of said interior being occupied by said noblegas for providing high operating gas pressure.
 7. Apparatus as describedin claim 5 wherein: said ceramic material is comprised ofpolycrystalline alumina, and said metal tubes are comprised of aniron-nickel-cobalt alloy adapted to permanent hermetic sealing topolycrystalline alumina.
 8. Apparatus as described in claim 7 wherein:said electrode support means are comprised of nickel, and said springmeans are comprised of a tungsten-rhenium alloy.